Abstract

It is well known that, after laying, hen egg albumen undergoes a liquefaction process that is usually referred to as "thinning". Despite the widespread use of this phenomenon for inferring egg quality (i.e. through the measure of the Haugh index), not many research groups have faced the challenging problem of explaining the relation between thinning and the molecular changes which take place in the albumen structure during aging.

Some proposals have been put forward along the years. Thinning has been explained as the result of an enhanced interaction between lysozyme and ovomucin caused by the change in the albumen pH from about 7 to about 9 after egg laying. The effect of pH has also been considered as responsible for the chemical cleavage of the O-glycoside link between trisaccharides and beta-ovomucin. Cleavage of this highly hydrophylic moiety would greatly reduce the interactions between ovomucin and water, thus causing the collapse of the albumen structure. In another explanation albumen thinning was again related to the pH raise through ovomucin de-polymerization. Although the above proposals are all supported by experimental data, no general agreement seems to have been reached among the researchers about the very reasons that bring about the albumen liquefaction.

In this work we supplement the available literature with new experimental data which were obtained by field cycling relaxometry using albumen samples from oiled and not-oiled eggs. Such data provide a different point of view for the comprehension of the thinning phenomenon. They also show that FC NMR relaxometry may contribute to understanding the processes of egg aging and of the various methods used to slow down its rate.